What is the "Mashup"?

In technology, a mashup is a web application that combines data from more than one source into a single integrated tool; an example is the use of cartographic data from Google Maps to add location information to real-estate data from Craigslist, thereby creating a new and distinct web service that was not originally provided by either source.
Mashup originally referred to the practice in pop music (notably hip-hop) of producing a new song by mixing two or more existing pieces.